The move comes in response to a complaint by Dutch Christian Democrat MEP Wim van Velzen, who was told he must provide a Belgian identity card or apartment lease before he could get a Belgian mobile phone subscription.

The MEP said that although two of the Belgian operators, Proximus and Mobistar, normally relent if customers give proof of a foreign home address, the third national mobile firm, Orange, charges non-Belgians a 173 euro deposit before they are allowed to ‘roam’ with their phone in other countries.

Bolkestein said the European Commission could not take the Belgian government to court for a breach of single market rules because the demands are imposed by telecom firms and not the state.

But he said such requirements – meant to stop fraud – were illegal and should be deemed “null and void” following a recent judgement of the European Court of Justice. It ruled that firms could not take steps to scupper the single market. Bolkestein added that “proof of identity with an indication of a bank account or credit card number would normally be sufficient for the operators”.

Many MEPs and other workers who make regular trips to attend meetings of the European Parliament and EU institutions get Belgian mobile phone subscriptions to save the expense of making international calls on a mobile when they are in Brussels. The same concerns would apply to temporary workers – such as the legions of IT contractors – who work across borders for part of the year.

Van Velzen said this week he would press the Commissioner to step in to force the companies to end their unfair practices. The Commission is already probing the ‘roaming charges’ of some EU operators. DG Competition raided the offices of UK and Germany operators earlier this year, seeking evidence of illegal behaviour.